1. Field of the Invention
This invention relates to an interchangeable lens provided with an automatic focusing device, and more particularly to an interchangeable lens in which a portion of a focusing phototaking lens is made removably mountable on a forward portion or a rearward portion of the lens barrel and the movement of the removably mountable phototaking lens is controllable by the automatic focusing device.
2. Description of the Prior Art
A device and system in which the distance of an object to be photographed is detected and made into an electrical signal transformed into a binary form while, on the other hand, the set distance of the distance adjusting ring of an interchangeable lens is taken out as an electrical signal transformed into a binary form and the information of the distance ring is compared with the object distance information and the movement of the distance ring is controlled by drive means such as a motor or the like whereby the phototaking lens is driven to its in-focus position have already been proposed by the assignee of the present invention in his U.S. application Ser. Nos. 944,974, now U.S. Pat. No. 4,305,657 and 121,690, now U.S. Pat. No. 4,329,033.
Today, there are known a number of cameras having autofocus devices and particularly, a typical example of the focusing system, as described in Japanese Laid-open Patent Application No. 92127/1975, is such that an automatic focus detecting mechanism is provided within a phototaking lens system and the whole or part of the phototaking lens is driven by the signal from the automatic focus detecting mechanism. Another typical example is disclosed in Japanese Laid-Open Patent Application No. 66223/1978 or No. 66224/1978 wherein a distance measuring device is provided outside the phototaking lens system and the whole or part of the phototaking lens is driven by a driving signal. These systems are directed chiefly for use in cameras such as 8 mm cameras or lens shutter cameras having a phototaking lens fixed to the camera body. However, these systems are entirely unsuitable for still single lens reflex cameras using a variety of interchangeable lenses, because a driving mechanism must be provided for each interchangeable lens and this leads to a heavy weight and expensiveness of the lens itself.
In a lens the whole of which is axially moved, smooth focusing cannot be effected because of the heavy weight of the lens itself. The amount of axial movement for a finite distance differs from one interchangeable lens to another and therefore, in the case of extraneous distance measurement, there must be newly provided a circuit for calculating the amount of axial movement corresponding to each lens.